Low polydispersity glycidyl azide polymer

ABSTRACT

Epichlorohydrin is polymerized in the presence of anhydrous stannic chloride catalyst and an alcohol initiator to produce a polyepichlorohydrin product comprising predominantly secondary hydroxyl-terminated polyepichlorohydrin polymer having low polydispersity, from which polyurethanes and azide derivatives can be made, polyurethanes prepared from such azide derivatives being useful as a binder for solid rocket propellants.

This is a division of application Ser. No. 06/750,910 filed Jul. 1,1985, now U.S. Pat. No. 4,879,419.

This invention relates to hydroxyl-terminated polymers ofepichlorohydrin and their preparation. In another aspect, it relates toazide derivatives of said polymers. In another aspect, it relates topolyurethanes of said epichlorohydrin polymers and their azidederivatives. In a still further aspect, it relates to solid rocketpropellants using as a binder a polyurethane prepared from glycidylazide polymers derived from polyepichlorohydrin.

The acid-catalyzed (or cationic) ring-opening or polymerization ofepichlorohydrin in the presence of initiators, mainlyhydroxyl-containing molecules, e.g., water or alcohols (includingpolyols), to yield hydroxyl-terminated epichlorohydrin derivatives, isknown. U.S. Pat. No. 4,340,749 (Patel), U.S. Pat. No. 4,391,970(Okamoto) and U.S. Pat. No. 4,431,845 (Young et al) describe some recentimprovements. The first reference discloses the reaction offluoro-aliphatic alcohols with epichlorohydrin, and use of stannicchloride as a catalyst, to prepare fluoroaliphatic, hydroxyl-terminatedepichlorohydrins containing more than 25 wt. % carbon-bonded fluorine.The other two references disclose polymerization of epichlorohydrin inthe presence of water or a hydroxyl material (e.g. ethylene glycol) anda catalyst (in the Young et al patent, a fluorinated acid and apolyvalent organo tin compound such as diphenyl-dibutyl tin). Other artis U.S. Pat. No. 2,327,053 (Marple et al) and U.S. Pat. No. 2,380,185(Marple et al) which disclose reacting epichlorohydrin with an excess ofhydroxy compounds, such as isopropyl alcohol, in the presence of a metalhalide, such as stannic chloride, to produce mono-adducts rather thanpolymers. When known catalysts are used in concentrations to providecomplete conversion in a short reaction period, the product is typicallydark color.

Although the hydroxyl-terminated polyepichlorohydrin polyols preparedfollowing the procedures described in some of the art produce polymerproducts which are useful in some applications, they generally containundesirable amounts, e.g. up to 10 to 20 weight percent, of lowmolecular weight, non-hydroxyl functional, cyclic ether oligomers(comprising 2 or 4 epichlorohydrin units) as impurities or by-productswhich increase in amount as the molecular weight of thepolyepichlorohydrin product increases. The formation of cyclic oligomersis unfortunately characteristic of cationic ring-opening polymerizationsof cyclic ethers (E. J. Geothals, Adv. Polym. Sci., 23, 104 (1977)), andtime-consuming fractionation or extraction of the products may have tobe used if one desires to remove such impurities from the polymerizate.Furthermore, prior art methods often result in polyepichlorohydrinpolymer products having relatively high polydispersity (the ratio ofweight average molecular weight, M_(w), to number average molecularweight, M_(n)), which means, for example, that polyurethanes preparedfrom such products generally will not have physical properties ofdesired values.

Azide derivatives of hydroxyl-terminated polyepichlorohydrin polymers,i.e. glycidyl azide polymers prepared by reaction of suchpolyepichlorohydrins with inorganic azide, have been proposed inpreparing energetic binders for solid propellants (see, for example,U.S. Pat. No. 4,268,450 (Frankel et al) and U.S. Pat. No. 4,486,351(Earl)). The presence of the oligomer impurities in the glycidyl azidepolyol derivatives detracts from the physical properties of thepropellant binders prepared from them.

This invention provides, in one aspect, a process for the preparation ofnovel polyepichlorohydrin product comprising predominately secondaryhydroxyl-terminated polyepichlorohydrin polymer the by polymerization ofepichlorohydrin in the presence of anhydrous stannic chloride, SnCl₄, asa polymerization catalyst, and, as an initiator, an alcohol, preferablyan organic polyol, which is unreactive with the catalyst, and,preferably, a strong carboxylic acid (i.e., one having a pK_(a) of lessthan about 2, preferably less than about 1) as a co-catalyst, such astrifluoroacetic acid or trichloroacetic acid. The polyepichlorohydrinpolymer preferably has epichlorohydrin (or chloromethylethyleneoxy)units as essentially the only repeating units in the polymer and has ahydroxyl functionality, mainly or essentially in the form of --CH₂CH(CH₂ Cl)OH, of up to 4 or more. The product is generally normallyliquid and has a number average molecular weight, for example, of 500 to10,000, and a relatively narrow molecular weight distribution or lowpolydispersity, which is generally less than 1.5, preferably less than1.2, e.g. less than about 1.5 for a 2000 molecular weight product andeven less than about 1.2 for such product if the co-catalyst is used.The polyepichlorohydrin product contains only a relatively minor amount,e.g. less than 2 weight percent, per 1000 molecular weight of product,of low molecular weight, non-hydroxyl functional, cyclic ether oligomerswhich generally have 2 or 4 epichlorohydrin units cyclized, oressentially none of such oligomer if said co-catalyst is used. And theproduct is light colored, e.g. with a Gardner color of less than 2.

The process is outlined in the following equation where R(OH)_(m)represents the initiator. ##STR1## minor amount (if any) of oligomer. Inthe above equation, R is an organic radical, e.g. containing 1 to 20carbon atoms, such as an aliphatic radical or aromatic radical orcombination of such radicals, which can contain or be substituted withmoieties that are unreactive with epichlorohydrin or desired product anddo not adversely affect the polymerization or desired product, such ashalo, oxy, carbonyl, or combinations of such moieties, e.g., ester. Forexample, R can be CH₃ --, ClCH₂ CH₂ --, CH₃ CH₂ CH₂ CH₂ --, C₆ H₅ CH₂--, --CH₂ C₆ H₁₀ CH₂ --, --(CH₂)_(x) --where x is 3-8, --CH(R")CH(R')--and --CH(R')CH₂ CH(R')-- where R' is selected from H and a lower alkyl,such as CH₃ --, CH₂ Cl--, and C₂ H₅ --, and R" is said lower alkyl,##STR2## where x+y is 1 to 20, --CH₂ C₆ H₄ CH₂ --, CH₃ C(CH₂ --)₃. Thesubscript m is 1, 2, 3 or 4, and n is at least 2 and, where R has amolecular weight of less than 1000, n is a number such that thepolyepichlorohydrin, i.e. poly(chloromethylethyleneoxy), portion of theproduct is the major portion of the product by weight, n generally being2 to about 100.

Polyglycidyl azide polymer derivatives, described hereinafter, of thepolyepichlorohydrin polymers can be represented by a formula like "I" inthe above equation except that Cl is replaced by N₃. Such derivativeswill generally have approximately the same low polydispersity and lowoligomer content as the polyepichlorohydrin precursor.

The strong carboxylic acid used as a co-catalyst generally increases thepolymerization reaction rate as compared to the reaction rate obtainedwhen it is not used, i.e. when just the stannic chloride catalyst isused; for example, the time for complete conversion at 65°-70° C. of theepichlorohydrin is reduced from about 24 hours to 1 hour when theco-catalyst is used with the stannic chloride. The use of theco-catalyst with the stannic chloride also allows a lower amount ofstannic chloride catalyst to be used, e.g. to about 1/3 the amount. Andthe use of the co-catalyst, which speeds up the reaction rate, stillgenerally results in a hydroxyl-terminated polyepichlorohydrin reactionproduct of light color, e.g. a Gardner color of less than 2, and lowpolydispersity, and with lower amounts, if any, of the cyclic etheroligomers as compared to when the stannic chloride is used as the onlycatalyst.

The initiators used in the process of this invention are those which areunreactive with the stannic chloride. Representative illustrativeinitiators which can be used include monohydric aliphatic alcohols, suchas CH₃ OH, C₂ H₅ OH, (CH₃)₂ CHOH, CH₃ (CH₂)₃ OH, ClC₂ H₄ OH, and CH₃(CH₂)₁₆ CH₂ OH, monohydric cycloaliphatic alcohols, such as C₆ H₁₁ CH₂OH, polyhydric aliphatic alcohols, such as CH₂ (CH₂ OH)₂, HOCH₂CH(CH₃)OH, C₂ H₄ (CH₂ OH)₂, HOCH₂ CH(CH₂ Cl)OH, and CH₃ CH(OH)C₂ H₄ OH,aromatic alcohols, such as C₆ H₅ CH₂ OH, and polyhydric cycloaliphaticalcohols, such as ##STR3## and the hydroxyl-containing organic compoundsdisclosed in said U.S. Pat. No. 2,327,053 which are unreactive withstannic chloride.

Initiators which are polymeric in nature can also be used, such as a lowmolecular weight hydroxyl-functional polyepichlorohydrin,hydroxyl-functional poly(ethyleneterephthalate), hydroxyl-functionalperfluoropoly(oxyalkylene), such as HOCH₂ CF₂ O(CF₂ O)_(x) (CF₂ CF₂O)_(y) CF₂ CH₂ OH, hydroxyl-functional poly(oxyethylene), andhydroxyl-functional poly(oxypropylene). Other hydroxyl-containingorganic monomeric or polymeric materials which can be used are thosedisclosed in said U.S. Pat. No. 4,431,845 which are unreactive withstannic chloride. Fluoroaliphatic alcohols which can be used are thosesuch as C₈ F₁₇ SO₂ N(C₂ H₅)CH₂ CH₂ OH and C₈ F₁₇ SO₂ N(CH₂ CH₂ OH)₂, andthose disclosed in said U.S. Pat. No. 4,340,749 which are unreactivewith stannic chloride.

Mixtures of such initiators also can be used.

The applicability of an alcohol or hydroxyl-containing organic materialas an initiator for purposes of this invention can be simply determinedby mixing 1 part of anhydrous stannic chloride with 5 to 10 parts of thehydroxyl material in about 30 parts of 1,2-dichloroethane solvent,heating the resulting mixture, e.g. 70° C. for 1 hour, and observingwhether an irreversible reaction occurs, for example by evidence of aprecipitate or evolution of hydrogen chloride. If no such reactionoccurs, the hydroxyl material can be used as an initiator. Materialswhich have been found to be so reactive, and thus not suitable as aninitiator, include ethylene glycol.

Where the stannic chloride is used in the process of this inventionwithout the co-catalyst, 1,4-butane diol is not a preferred initiatorsince the use of the diol results in appreciable amounts of oligomer(see Example 5).

By controlling the proportions of epichlorohydrin to initiator, it ispossible to limit the degree of polymerization and, consequently, themolecular weight of the polyepichlorohydrin product of the invention.Thus, the molar ratio of epichlorohydrin to hydroxyl group in theinitiator may be in the range of about 2:1 to 100:1.

The stannic chloride catalyst employed in the process is a hydrolyzablecompound in the presence of water. Furthermore, its catalytic activityis considerably impaired when it is in a hydrolyzed condition and largeramounts of such catalyst are required to effect the polymerizationreaction when the reactants contain appreciable amounts of water ascompared to when they are substantially dry. Also, the hydrogen chlorideliberated by the hydrolysis of the stannic chloride may combine with theepichlorohydrin to form chlorohydrin by-products which may undesirablyact as initiators. It is therefore preferable that the reactants used inthe process of the invention be in substantially anhydrous condition.

The amount of stannic chloride catalyst to be used in the process ofthis invention without the co-catalyst is that amount sufficient toresult in generally substantially quantitative or preferably essentiallycomplete conversion of the epichlorohydrin to the polyepichlorohydrinproduct, and the amount of stannic chloride to be used will depend onthe desired molecular weight of such product. Generally, for a producthaving a desired molecular weight of about 2000, such amount of stannicchloride will be about 0.5 to 1 weight percent of the polymerizationreaction mixture; for a product with a molecular weight of 4000, suchamount of stannic chloride will be about 1 to 2 weight percent; and fora product with a molecular weight of 1000, such amount will be about0.25 to 0.5 weight percent.

As discussed above, the preferred process of this invention employs astrong carboxylic acid as a co-catalyst. Where such co-catalysts areused, 1,4-butane diol can be used as initiators without resulting in theformation of appreciable amounts of the cyclic oligomer.

Generally, the strong carboxylic acid co-catalyst used in this inventionare those having a pK_(a) of less than 2 and preferably less than 1, asdetermined, for example, by the method described by W. Huber, "Titrationin Nonaqueous Solvents," Academic Press, New York, N.Y., 1967, p. 215. Aclass of such acid co-catalysts can be represented by the formulaR--CXY--COOH, where X and Y are independently selected from the groupconsisting of chlorine and fluorine, and R is hydrogen, fluorine,chlorine, or a moiety which is electron-withdrawing (relative tohydrogen), e.g. --C₂ F₅ and --C₆ H₅, and does not adversely affect thepolymerization. Representative co-catalysts (and their pK_(a) values)include trifluoroacetic acid (0.23), trichloroacetic acid (0.66), anddichloroacetic acid (1.25).

The amount of co-catalyst used in this invention is that which, togetherwith the stannic chloride catalyst, is sufficient to minimize theformation of the cyclic ether oligomeric by-products. Such amountgenerally will also, as compared to using the stannic chloride as thesole catalyst, increase the reaction rate and permit use of less stannicchloride. Generally, the molar ratio of stannic chloride to co-catalystwill be 1:0.5 to 1:10, preferably 1:3 to 1:5, higher amounts of theco-catalyst in these ranges acting significantly as an initiator andthus influencing the molecular weight of the polyepichlorohydrinproduct.

The process of this invention can be carried out in the presence of asolvent or inert diluent, for example where the alcohol initiator is asolid, suitable solvents for this purpose representatively including1,2-dichloroethane, benzene, toluene, methylene chloride, and carbontetrachloride. The catalyst(s) can be added to the reaction vesselcontaining the initiator and solvent and the epichlorohydrin can be thenincrementally added. Prior to adding the epichlorohydrin, and during itsaddition and the ensuing reaction, the reaction vessel is heated orcooled to a desired polymerization temperature, e.g. about 0° C. to 110°C., preferably 65° to 75° C. The polymerization reaction is conductedunder anhydrous conditions and to that end a slow, dry nitrogen gaspurge of the reaction vessel can be used. The reaction pressure isgenerally the autogenous pressure but superatmospheric pressures can beused, e.g. up to 10 atmospheres, where the more volatile initiators areused.

Generally, completion of the reaction will be indicated by the cessationof the reaction exotherm and the leveling-off of the viscosity increaseof the reaction mixture. Completion of the reaction can be verified bymeasuring the weights of reaction mixture samples before and after theyare heated to remove volatile materials.

The resulting secondary hydroxyl-terminated polyepichlorohydrin productcan be recovered by subjecting the reaction product mixture to reducedpressure to remove solvent and volatile material, e.g. unreactedepichlorohydrin, adding further solvent, and then extracting thenon-volatile material with an extracting agent, such as aqueous organicsolvent, e.g. alcohol such as methanol or a ketone such as acetone,containing ammonium hydroxide, or preferably a chelating agent for tinsuch as the tetrasodium salt of ethylenedinitrilotetraacetic acid, usedin an amount of about 5 to 10 percent in excess of the equivalent amountnecessary to complex with the stannic chloride and neutralize the acidco-catalyst (if present). The resulting two phases are separated, theheavier phase containing the desired polyepichlorohydrin product and theother phase being the aqueous organic solvent containing the chelatingagent and catalysts. The product phase can be washed several additionaltimes with aqueous organic solvent. The washed product can be strippedunder reduced pressure.

The recovered polyepichlorohydrin product typically has a Gardner colorof less than 2 and is lighter in color than the crude product. Suchlight-colored product is advantageous in that it indicates to apurchaser of it that it is of high purity and it can be used inapplications (e.g. optics) where such light color is a requirement.

The conversion of the epichlorohydrin to the desired secondaryhydroxyl-terminated polyepichlorohydrin product by the process of thisinvention is generally substantially quantitative and usually at least95 percent based on the epichlorohydrin reactant, and typically 98 to100 percent when the co-catalyst is used with the stannic chloride. Theamount of the cyclic oligomer by-product is a minor amount of thepolyeipchlorohydrin product, generally less than 2 weight percent per1000 molecular weight of product and, in the case where the co-catalystis used with the stannic chloride, less than 0.5 weight percent per 1000molecular weight of product.

The secondary hydroxyl-terminated polyepichlorohydrin products of thisinvention can be reacted with chain extension agents or crosslinkingagents, such as polyfunctional compounds reactive with hydroxyl groups.For example, the products can be reacted with polyisocyanates, e.g.,p-phenylene diisocyanate, 2,4- and/or 2,6-tolylene diisocyanates, in aconventional urethane reaction (e.g., see said U.S. Pat. Nos. 4,340,749and 4,405,497) to form elastomeric polyurethanes useful as foams forupholstery, automobile bumpers, and high performance coatings, orreacted with tertiary amines to form water-soluble polymeric quaternarysalts used as plating bath additives.

The polyepichlorohydrin products of this invention can also be reactedin a conventional manner with inorganic or metal azides, such as sodiumazide, to form normally liquid, secondary hydroxyl-terminatedpolyglycidyl azide polymers used as energetic binders or plasticizersfor solid gun propellants, for example by the procedures described inU.S. Pat. No. 4,268,450 (Frankel et al), U.S. Pat. No. 4,288,262(Flanagan), U.S. Pat. No. 4,379,894 (Frankel et al), and U.S. Pat. No.4,486,351 (Earl).

The low content of the cyclic oligomer by-product in thepolyepichlorohydrin product of this invention is advantageously carriedover to the derivatives thereof, such as polyglycidyl azide polymerderivative product, together with the relatively low polydispersityproperty, thus the derivatives will have mechanical or physicalproperties which enhance their use, e.g. as energetic propellant bindersor plasticizers.

In using the polyglycidyl azide polymer derivative products for use insolid rocket propellants, they can be mixed with an optional liquidplasticizer and then with solid particulate oxidizer, polyisocyanatecuring agent, optional other fuel components, bonding agents, processingaids, burn rate catalysts, cure catalysts, carbon black, and combustionstabilizers. The propellant ingredients can be blended in a slow speed,high-shear mixer until all the solid particles are wetted by the liquidsin the system, the mixing optionally being carried out under vacuum toremove trapped air. The polyisocyanate curing agent is then added. Anadditional short mixing cycle is completed. The viscous, uncuredpropellant slurry can be transferred into a prepared rocket motorcasing. The filled casing can then be slowly heated to the appropriatecure temperature (generally 55° to 80° C.) and held at that temperatureuntil the urethane reaction has taken place and the liquid binderprecursor is converted to a solid, elastomeric polyurethane matrixproviding mechanical integrity, environmental protection, and acontrolled burning surface to the resulting solid propellant. Suchpropellants can be used in aircraft starter cartridges and ducted rocketboosters, and as low signature propellants, minimum smoke propellant,and gun propellants.

Further details on the preparation of the above-described polyurethanesand their use as binders for solid rocket propellants will be omitted inthe interest of brevity, since the steps in preparing them arewell-known, e.g. see U.S. Pat. No. 3,642,705 (Zollinger) whosedisclosure is incorporated herein by reference for such purpose.

Objects and advantages of this invention are illustrated in thefollowing examples.

EXAMPLE 1

To a 5-L, 3-neck flask equipped with an electric heating mantle,stirrer, thermometer, condenser, addition funnel, and gas inlet tube wasadded 273 g 1,2-dichloroethane solvent and 75.5 g1,4-bis(hydroxymethyl)cyclohexane initiator. A slow, dry nitrogen gaspurge was started and maintained throughout the reaction and solventstripping operation. To the well-stirred solution heated to 65° C. wasadded, by means of a syringe, 15 g stannic chloride. The heating mantlewas removed and 2,652 g epichlorohydrin was added with stirring over atwo-hour period while maintaining the reaction temperature at 65°-70° C.by controlling the rate of addition and the use of a water-ice bath.After the addition was complete, the reaction mixture was stirred at 65°to 70° C. for an additional 24 hours. A small, weighed sample of thereaction mixture was heated for 1 hour at 105° C. in a vented oven toremove volatile material, and the heated sample then weighed, thedifference in weights indicating 98% conversion of epichlorohydrin tohydroxyl-terminated polyepichlorohydrin product. Solvents and volatilematerials were removed at 65° C. under reduced pressure (5 torr) over asix-hour period. A small product sample (1A) was removed for analysis.The remainder of the crude product was dissolved in 600 g1,2-dichloroethane, and 1500 g of a 10% aqueous methanol solutioncontaining 30 g of ethylenedinitrilotetraacetic acid, tetrasodium salt,added, and the mixture stirred vigorously for two hours at 60° C. Themixture was cooled to room temperature and the lower phase of the twoliquid phases was separated and extracted with 1500 g 10% aqueousmethanol at 60° C. The phases were separated as before and the lowerphase extracted again with 1500 g of 10% aqueous methanol at 60° C. Thelower phase, which separated, was stripped of solvent and volatiles at 5torr over a six-hour period to yield 2122 g of the purified, liquidpolyepichlorohydrin diol having the following structure: ##STR4##

The molecular weight of the purified polyepichlorohydrin product wascalculated to be 5200, based on the epichlorohydrin used. The molecularweight found was about 4000 (determined from equivalent weight bytitration with phenyl isocyanate). Oligomer content of this purifiedpolymer determined by gel permeation chromatography was 2.7 wt. %compared with 4.7 wt. % for the crude product (sample 1A above beforepurification).

EXAMPLES 2-7

Additional preparations of polyepichlorohydrin diol products of thisinvention, comprising liquid polyepichlorohydrin diols having structureswithin the scope of formula I, supra, where m is 2, were made followingthe general procedure of Example 1 and utilizing catalyst/initiatorsystems of this invention. The reagents employed and the molecularweights and cyclic oligomer content of the resulting products are shownin Table 1 below together with that of Example 1. Comparative ExamplesC-1 to C-5, employing prior art catalyst and initiators, are alsoincluded in Table 1.

                                      TABLE 1                                     __________________________________________________________________________                               Polyeipchlorohydrin                                                           diol product                                                                           Oligomer                                  Epichlorohydrin,                                                                         Catalyst                                                                              Initiator                                                                             Mol. Wt..sup.c.                                                                        content,.sup.d.                           Ex.                                                                              g       Code.sup.a.                                                                       g   Code.sup.b.                                                                        g  Nominal                                                                            Found                                                                             wt. %                                     __________________________________________________________________________    1  2652    A   15  BHMC 75.5                                                                             5200 3940                                                                              4.7                                       2  2536    A   12  BHMC 165.3                                                                            2000 1876                                                                              <0.5.sup.e.                               3  1891    A   8   PD   22 6000 4928                                                                              6.4.sup.f.                                4  1168    A   5.4 PD   8.4                                                                              9000 6686                                                                              8.4.sup.g.                                5  1088    A   5.6 BD   22.5                                                                             4000 --  28.5.sup.h.                               6  1157    A   5.3 PD   19 4000 3770                                                                              5.8                                       7  2674    A   15  BHMC 86.4                                                                             4000 --  3.0                                       C-1                                                                               546    B, C                                                                              2.0, 1.0                                                                          PECH-D                                                                             180                                                                              2000 2180                                                                              --                                        C-2                                                                              2300    B, C                                                                              5.0, 2.5                                                                          PECH-D                                                                             200                                                                              6000 3314                                                                              11.3                                      C-3                                                                              1170    B, C                                                                              5.3, 2.7                                                                          EG   6.9                                                                              9000 5926                                                                              13.6                                      C-4                                                                               928    B, C                                                                              8.0, 4.0                                                                          BHMC 72 2000 --  5.8                                       C-5                                                                              1157    B, C                                                                              5.3, 2.7                                                                          PD   19 4000 3486                                                                              9.9                                       __________________________________________________________________________     .sup.a. A = SnCl.sub.4, B = (nC.sub.4 H.sub.9).sub.2 Sn(C.sub.6               H.sub.5).sub.2, C = (CF.sub.3 SO.sub.2).sub.2 CH(C.sub.6 H.sub.5)             ##STR5##                                                                      BD = HO(CH.sub.2).sub.4 OH,                                                   EG = HOCH.sub.2 CH.sub.2 OH,                                                  PECHD = a low mol. wt. polyepichlorohydrin polyol prepared as in Ex. 1        except no solvent was used and the following reagents were used: 896 g        epichlorohydrin, 103 g ethylene glycol initiator, 2.0 g catalyst B, and       1.0 g catalyst C.                                                             .sup.c. Nominal or target mol. wt. is based on amounts of diol initiator      and epichlorohydrin used; "Found" mol. wt. is two times the hydroxyl          equivalent wt. determined by titration with phenyl isocyanate.                .sup.d. Before extraction.                                                    .sup.e. "<0.5" signifies that no detectable amount of oligomer was            observed by the gel permeation procedure used.                                .sup.f. After extraction, the oligomer content was 1.6 wt %. The              extraction was carried out as in Example 1, except that ammonium hydroxid     was used instead of the tetrasodium salt.                                     .sup.g. After 3 extractions of the product with aqueous methanol, the         oligomer content was <0.5 wt %.                                               .sup.h. If the reaction of this example had included cocatalyst, the          oligomer content would have been <0.5 wt %.                              

The lower "found" molecular weights for the diol products are believeddue to small amounts of water (present in the epichlorohydrin monomer)which acts as an additional initiator and thus contributes to the lower"found" molecular weight value.

Table 1 shows the decreased amount of oligomer obtained using the SnCl₄catalyst of this invention compared with a prior art catalyst system;this is shown by comparing products of similar molecular weights, viz.Ex. 2 vs. C-4, Ex. 6 vs. C-5, Ex. 3 vs. C-2, and Ex. 4 vs. C-3.

EXAMPLE 8

A. To a flask equipped as in Example 1 was added 40 g1,2-dichloroethane, 7.2 g 1,4-bis(hydroxymethyl)cyclohexane, and 4.0 mlof a 1,2-dichloroethane solution containing 0.84 g SnCl₄ and 1.74 g CF₃COOH co-catalyst. To this stirred solution was added 222.7 g ofepichlorohydrin over a 35-minute period and the temperature wasmaintained at 65°-70° C. by cooling the flask. During the addition, thesolution turned from clear to pink to blue and finally to a dark purplecolor. After an additional 30 min. of stirring at 65°-70° C., thereaction mixture was cooled to room temperature and a small sample (A1)was removed for analysis. The remainder of the reaction mixture wasextracted with 100 g of a 10% aqueous methanol solution containing 2 gof the sodium salt of ethylenedinitrilotetraacetic acid and 0.5 g ofconcentrated aqueous NH₄ OH, the extraction causing dissipation of thepurple color. The resulting light-colored, organic phase was extractedwith two 100 g portions of 10% aqueous methanol solution and thenstripped of solvent and volatiles at 65°-70° C. and 5 torr over a 4-hourperiod to yield the liquid hydroxyl-terminated polyepichlorohydrin (A2)comprising polymer having a structure like that shown in Example 1.

B. The above reaction was repeated except the CF₃ COOH was omitted. Atthe end of the addition of epichlorohydrin, a considerable amount of itremained unreacted, so heating at 65° C. was continued for a total of 23hours. After cooling to room temperature, a sample of the reactionmixture (B1) was removed for analysis. The remainder of the reactionmixture was extracted as above except that NH₄ OH was omitted in thefirst extraction. The washed organic phase was stripped of solvent asabove to yield the liquid hydroxyl-terminated polyepichlorohydrin (B2)product comprising polymer having the structure shown in Example 1.

Analysis of the above polymeric products are summarized in Table 2.

                  TABLE 2                                                         ______________________________________                                              Hydroxyl                        Oligomer                                      equivalent               Poly-  content,                                Product                                                                             weight     M.sub.n.sup.b                                                                        M.sub.w.sup.b                                                                        dispersity.sup.c                                                                     wt. %                                   ______________________________________                                        A1    --         1842   2201   1.19   0                                       A2    1560       1934   2245   1.16   0                                       B1    --         1861   2656   1.42   4.3                                     B2    1870       1963   2595   1.32   2.8                                     ______________________________________                                         .sup.a Determined by phenyl isocyanate titration.                             .sup.b Determined by gel permeation chromatography (polypropylene glycol      standard)                                                                     .sup.c M.sub.w /M.sub.n                                                  

EXAMPLE 9

Example 8A was repeated except that twice the quantity of initiator(14.4 g) and one-half the amount of catalyst solution (2.0 ml) wereemployed. The epichlorohydrin addition took 1 hour: the dark purplecolor of the reaction mixture changed to a pale yellow near the end ofthe addition. Samples of the polyepichlorohydrin product taken afterreaction (Ex. 9-1) and after extraction and stripping (Ex. 9-2) wereanalyzed. The results are summarized in Table 3.

                  TABLE 3                                                         ______________________________________                                               Hydroxyl                        Oligomer                                      equivalent               Poly-  content,                               Example                                                                              weight     M.sub.n                                                                              M.sub.w                                                                              dispersity                                                                           wt. %                                  ______________________________________                                        9-1    --         1420   1553   1.094  0                                      9-2    910        1462   1604   1.096  0                                      ______________________________________                                    

EXAMPLES 10-19

These examples describe the results of employing various dihydroxyinitiators with the tin tetrachloride/trifluoroacetic acid catalystsystem in polymerizing epichlorohydrin (in 25 g 1,2-dichloroethane)according to this invention following the general procedure of Example8A. In each example, the reaction was carried out by adding theepichlorohydrin over a 30-min. period and at 70° C. for 1 hr. Thereactants, amounts, approximate conversion, and product analyses aresummarized in Table 4. The liquid diol polymers of each example hadstructures falling within the scope of formula I, supra.

                  TABLE 4                                                         ______________________________________                                                       EXAMPLE                                                                       10    11      12      13                                       ______________________________________                                        Reaction mixture                                                              Initiator (0.10 mole), g                                                       ##STR6##        14.4                                                         HO(CH.sub.2).sub.3 OH    7.6                                                  HO(CH.sub.2).sub.4 OH            9.0                                          HOCH.sub.2 CH(CH.sub.3)OH              11.0                                   SnCl.sub.4, g    0.63    0.84    0.63  0.63                                   CF.sub.3 COOH cocatalyst, g                                                                    1.36    1.82    1.36  1.36                                   Epichlorohydrin, g                                                                             242     249     248   246                                    Color of reaction mixture                                                                      purple  pink    pink  tan                                    Conversion, wt % 100     100     100   100                                    Product analysis                                                              Hydroxyl equivalent wt..sup.a.                                                                 1530    1330    1540  1410                                   M.sub.n.sup.a.   1350    1360    1400  1540                                   M.sub.w.sup.a.   1530    1560    1700  1720                                   Polydispersity, M.sub.w /M.sub.n                                                               1.14    1.14    1.22  1.12                                   Oligomer content before extraction,                                                            0       0       0     0                                      wt. %                                                                         ______________________________________                                         .sup.a. Values given are those after extraction. Extracting agent used wa     like that used in Example 1.                                             

The results show that 1,3-propanediol, 1,2-propanediol, and 1,4-butanediol (Examples 11-13) are as effective as1,4-bis(hydroxymethyl)cyclohexane (Example 10) as initiators in thepolymerization of epichlorohydrin in high yields to apolyepichlorohydrin product free of oligomer and having a lowpolydispersity. However, under the same reaction conditions, usingethylene glycol instead of such initiators, a low yield (18%) ofpolyepichlorohydrin hydrin product resulted.

EXAMPLE 4

This example describes the preparation of a nominally 4000 molecularweight polyepichlorohydrin product following the general procedure ofExample 8A employing 60 g 1,2-dichloroethane, 3.3 g1,4-bis(hydroxymethyl)cyclohexane, 7 ml of a 1,2-dichloroethane solutioncontaining 1.47 g tin tetrachloride, 3.05 g trifluoroacetic acid, and213 g of epichlorohydrin. The reaction time was 1.5 hours at 70° C. (98%conversion). The reaction mixture was extracted with an aqueous methanolsolution as in Example 8A and the polyepichlorohydrin product wasisolated and upon being analyzed the hydroxyl equiv. wt. found to be1770, M_(n) was 2010, M_(W) was 2550, and polydispersity was 1.27. Therewas little if any oligomer in the product as indicated by gel permeationchromatography (no more than about 1% in any case). Proton nmr of theproduct indicated about 7% primary hydroxyl groups due to some polymerchains being initiated by trifluoroacetic acid which was later removedin the isolation procedure.

EXAMPLE 15

This example describes the preparation of a low molecular weightpolyepichlorohydrin having only one hydroxyl group at the end of eachpolymer chain by using a monohydroxy initiator molecule. The procedurefollowed was that of Examples 11-13, employing 25 g 1,2-dichloroethane,40.3 g 2-chloroethanol initiator, 3 ml of a 1,2-dichloroethane solutioncontaining 0.63 g tin tetrachloride and 1.36 g trifluoroacetic acid, and210 g of epichlorohydrin. The reaction conditions were 1 hour at 70° C.(97% conversion). The reaction mixture was extracted with 100 g of a 20%aqueous methanol solution containing 4 g of ethylenedinitrilotetraaceticacid, tetrasodium salt. The liquid polyepichlorohydrin product comprisesa mono-secondary hydroxyl-terminated polyepichlorohydrin polymer havinga structure falling within the scope of formula I, supra, where m is 1.The product was isolated and analysis showed the hydroxyl equiv. wt. was650, M_(n) was 430, M_(W) was 480, and polydispersity was 1.11. Therewas no oligomer indicated by gel permeation chromatography.

EXAMPLE 16

This example describes the preparation of the glycidyl azide polymerderivative of a polyepichlorohydrin product of this invention.

One hundred grams of the polyepichlorohydrin product prepared like thatof Example 2, dissolved in 100 g of dimethylsulfoxide (DMSO), was addedto a stirred slurry of 100 g of sodium azide in 230 g of DMSO. Themixture was heated to 80° C. and maintained at that temperature for 24hours and decanted from the precipitated salts into an equal volume ofcold water. The decanted mixture was heated to 80° C. and stirred for 2hours, the phases allowed to separate, the aqueous phase discarded, andthe water washing repeated twice more. Then 120 g of 1,2-dichloroethanewas added to the washed product and the resulting solution was washedthree times with 600 g portions of water. The separated organic phasewas stripped at 40°-50° C. and 5 torr with a slow N₂ purge for 6 hours,to yield a hydroxyl-terminated polyglycidyl azide polymer product havingthe structure ##STR7##

About 1 ml of the above azide polymer product was placed in adellagrating spoon and held just above a Bunsen burner flame, whereuponit rapidly (in a matter of a few seconds) disappeared in a red-glowingfireball with a "woof" sound. This shows that the product is energeticand indicates that it would be useful in preparing a polyurethane binderfor solid rocket propellants.

EXAMPLE 17

The polyepichlorohydrin product (10.6 g) of Example 2 was mixed at roomtemperature with 2 g of a polyisocyanate, DESMODUR N-100, and 1 drop ofa urethane catalyst, dibutyltin dilaurate. The mixture gelled to yield apolyurethane elastomer.

A sample of the polyurethane elastomer immersed in heptane in a closedbottle did not appear to gain weight over a period of months, showingthat it could be used to form solvent resistant articles, such as floorcoverings, gaskets, and hoses.

EXAMPLE 18

The polyglycidyl azide polymer product of Example 16 (11 g) was mixed atroom temperature with 2 g of DESMODUR N-100, and 4 drops of dibutyltindilaurate. The curable mixture gelled in 137 minutes to yield apolyurethane elastomer. A small piece of the cured elastomer was heldwith tweezers just above the flame of a burning wooden match, whereuponit partially vaporized without charting; the evolved vapors extinguishedthe flame. This indicates the utility of the elastomer as an energeticbinder for solid rocket propellants.

A film coating of the curable mixture in 1,2-dichloroethane was preparedand allowed to cure upon standing. The resulting cured coating could beremoved by hot air from an electric heat gun substantially withoutdamaging the polyester film substrate upon which the curable mixture wascast. This shows the polyurethane elastomer is useful as a thermallyreleasable coating.

Various modifications and alterations of this invention will becomeapparent to those skilled in the art without departing from the scopeand spirit of this invention.

What is claimed is:
 1. A normally liquid, polyglycidyl azide productsaid product being produced by reacting, with an inorganic azide, apolyepichlorohydrin product comprising predominantly secondaryhydroxyl-terminated polyepichlorohydrin polymer having a number averagemolecular weight of at least 2000, and a polydispersity of less than1.2, and essentially no non-hydroxyl functional cyclic ether oligomer;said polyepichlorohydrin product being made by polymerizingepichlorohydrin in the presence of anhydrous stannic chloride catalyst,a strong carboxylic acid co-catalyst, and an alcohol as an initiator. 2.The product of claim 1 wherein said product is normally liquid and saidpolyglycidyl azide polymer is represented by the formula ##STR8## whereR is an organic radical, m is 1 to 4, and n is at least
 2. 3. Theproduct of claim 2 wherein R is ##STR9##
 4. Elastomeric polyurethanecomprising the reaction product of the polyglycidyl azide product ofclaim 1 and polyisocyanate.
 5. A solid propellant comprising oxidizer,binder, and as a plasticizer the polyglycidyl azide polymer of claim 1.6. A solid propellant comprising oxidizer and an elastomericpolyurethane binder comprising the reaction product of the polyglycidylazide product of claim 1 and polyisocyanate.
 7. A process for thepreparation of polyglycidyl azide product, comprising reactingpolyepichlorohydrin product with an inorganic azide, saidpolyepichlorohydrin product comprising predominantly secondaryhydroxyl-terminated polyepichlorohydrin polymer having a number averagemolecular weight of at least 2000, and a polydispersity of less than1.2, and essentially no non-hydroxyl functional cyclic ether oligomer;said polyepichlorohydrin product being made by polymerizingepichlorohydrin in the presence of anhydrous stannic chloride catalyst,a strong carboxylic acid co-catalyst, and an alcohol as an initiator. 8.The product of claim 2, wherein R has 1 to 20 carbon atoms and is analiphatic radical, a cycloaliphatic radical, an aromatic radical orcombination of such radicals, m is 2 and n is 2 to
 100. 9. The productof claim 2, wherein R is --(CH₂)₃ --, --(CH₂)₄ --, or CH₂ CH(CH₃)-- andm is
 2. 10. The product of claim 2, wherein R is N₃ CH₂ CH₂ -- and mis
 1. 11. Elastomeric polyurethane comprising the reaction product ofpolyisocyanate and a polyepichlorohydrin product having a number averagemolecular weight of at least 2000 and a polydispersity of less than 1.2,said product comprising predominantly secondary hydroxyl-terminatedpolyepichlorohydrin polymer and essentially no non-hydroxyl functionalcyclic ether oligomer, said product being made by polymerizingepichlorohydrin in the presence of anhydrous stannic chloride catalyst,a strong carboxylic acid co-catalyst, and an alcohol as an initiator.